Referring to the M68 and X67, other than the size of the screen, please inform me how I will reap the benefits on a more expensive unit? The one I have now is accurate as can be. I see where side and down scan sonars are a huge help. But on a regular DF, what's the difference? The 565 and 570 HB units are good, so are the lowrance 480 and eagle 320 (which is on clearance now for $110)